Speed up toLowerCase, by manually inlining the upper-case part.

runtime/lib/string_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 
   /* patch */ const factory String.fromEnvironment(String name,
@@ skipping 761 matching lines @@
       for (int i = 0; i < delta; i++) {
         for (int j = 0; j < padLength; j++) {
           result._setAt(index++, padding.codeUnitAt(j));
         }
       }
     }
     return result;
   }
 
   // Lower-case conversion table for Latin-1.
+  // Upper-case ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.
+  // Conversion to lower case performed by adding 0x20.
   static const _LC_TABLE = const [
     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
     0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
     0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
     0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
     0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
     0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
     0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
     0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
     0x40, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
@@ skipping 15 matching lines @@
     0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
     0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
     0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xd7,
     0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xdf,
     0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
     0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
     0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
     0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
   ];
 
-  String _toLowerCaseUpperCaseDetectedAt(int firstUpperCaseIndex) {
-    // String contains upper case characters. Create a new string.
-    final length = this.length;
-    final result = _allocate(length);
-    // First up to firstUpperIndex.
-    int i = 0;
-    for (; i < firstUpperCaseIndex; i++) {
-      result._setAt(i, this.codeUnitAt(i));
-    }
-    for (; i < length; i++) {
-      result._setAt(i, _LC_TABLE[this.codeUnitAt(i)]);
-    }
-    return result;
-  }
-
   String toLowerCase() {
     for (int i = 0; i < this.length; i++) {
       final c = this.codeUnitAt(i);
-      // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.
-      if (c != _LC_TABLE[c]) {
-        return _toLowerCaseUpperCaseDetectedAt(i);
+      if (c == _LC_TABLE[c]) continue;
+      // Upper-case character found.
+      final result = _allocate(this.length);
+      for (int j = 0; j < i; j++) {
+        result._setAt(j, this.codeUnitAt(j));
       }
+      for (int j = i; j < this.length; j++) {
+        result._setAt(j, _LC_TABLE[this.codeUnitAt(j)]);
+      }
+      return result;
     }
     return this;
   }
 
   // Allocates a string of given length, expecting its content to be
   // set using _setAt.
   static _OneByteString _allocate(int length) native "OneByteString_allocate";
 
 
   static _OneByteString _allocateFromOneByteList(List<int> list)
@@ skipping 94 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }